Communication wire

ABSTRACT

The present invention relates to an improved isolated core or insulated conductor with a low dielectric constant and reduced materials costs. Apparatuses and methods of manufacturing the improved isolated core or insulated conductor are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/562,752,filed Sep. 18, 2009, which is a continuation of application Ser. No.12/154,284, filed May 20, 2008, which is a continuation of applicationSer. No. 11/800,038, filed May 3, 2007, now U.S. Pat. No. 7,560,648,issued Jul. 14, 2009, which is a continuation of application Ser. No.10/389,254, filed Mar. 14, 2003, now U.S. Pat. No. 7,214,880, issued May8, 2007, which is a Continuation-In-Part of application Ser. No.10/321,296, filed Dec. 16, 2002, now U.S. Pat. No. 6,743,983, issuedJun. 1, 2004, which in turn is a Continuation-In-Part of applicationSer. No. 10/253,212, filed Sep. 24, 2002, now abandoned, whichapplications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an improved wire and methods of makingthe same.

BACKGROUND OF THE INVENTION

One method of transmitting data and other signals is by using twistedpairs. A twisted pair includes at least one pair of insulated conductorstwisted about one another to form a two conductor pair. A number ofmethods known in the art may be employed to arrange and configure thetwisted pairs into various high-performance transmission cablearrangements. Once the twisted pairs are configured into the desired“core,” a plastic jacket is typically extruded over them to maintaintheir configuration and to function as a protective layer. When morethan one twisted pair group is bundled together, the combination isreferred to as a multi-pair cable.

In cabling arrangements where the conductors within the wires of thetwisted pairs are stranded, two different, but interactive sets oftwists can be present in the cable configuration. First, there is thetwist of the wires that make up the twisted pair. Second, within eachindividual wire of the twisted pair, there is the twist of the wirestrands that form the conductor. Taken in combination, both sets oftwists have an interrelated effect on the data signal being transmittedthrough the twisted pairs.

With multi-pair cables, the signals generated at one end of the cableshould ideally arrive at the same time at the opposite end even if theytravel along different twisted pair wires. Measured in nanoseconds, thetiming difference in signal transmissions between the twisted wire pairswithin a cable in response to a generated signal is commonly referred toas “delay skew.” Problems arise when the delay skew of the signaltransmitted by one twisted pair and another is too large and the devicereceiving the signal is not able to properly reassemble the signal. Sucha delay skew results in transmission errors or lost data.

Moreover, as the throughput of data is increased in high-speed datacommunication applications, delay skew problems can become increasinglymagnified. Even the delay in properly reassembling a transmitted signalbecause of signal skew will significantly and adversely affect signalthroughput. Thus, as more complex systems with needs for increased datatransmission rates are deployed in networks, a need for improved datatransmission has developed. Such complex, higher-speed systems requiremulti-pair cables with stronger signals, and minimized delay skew.

The dielectric constant (DK) of the insulation affects signal throughputand attenuation values of the wire. That is, the signal throughputincreases as the DK decreases and attenuation decreases as DK decreases.Together, a lower DK means a stronger signal arrives more quickly andwith less distortion. Thus, a wire with a DK that is lower(approaching 1) is always favored over an insulated conductor with ahigher DK, e.g. greater than 2.

In twisted pair applications, the DK of the insulation affects the delayskew of the twisted pair. Generally accepted delay skew, according toEIA/TIA 568-A-1, is that both signals should arrive within 45nanoseconds (ns) of each other, based on 100 meters of cable. A delayskew of this magnitude is problematic when high frequency signals(greater than 100 MHz) are being transmitted. At these frequencies, adelay skew of less than 20 ns is considered superior and has yet to beachieved in practice.

In addition, previously, the only way to affect the delay skew in aparticular twisted pair or multi-pair cable was to adjust the lay lengthor degree of twist of the insulated conductors. This in turn required aredesign of the insulated conductor, including changing the diameter ofthe conductor and the thickness of the insulation to maintain suitableelectrical properties, e.g. impedance and attenuation.

One attempt at an improved insulated conductor included the use of ribson the exterior surface of the insulation or channels within theinsulation but close to the exterior surface of the insulation. Theribbed insulation, however, was unsatisfactory because it was difficult,if not impossible, to make the insulation with exterior surfacefeatures. Because of the nature of the insulation material used and thenature of process used, exterior surface features would be indistinctand poorly formed. Instead of ribs with sharp edges, the ribs would endas rounded mounds. The rounded result is an effect of using materialsthat do not hold their shape well and of using an extrusion die to formthe surface features. Immediately after leaving the extrusion die, theinsulation material tends to surge and expand. This surging rounds edgesand fills in spaces between features.

Insulated conductors with ribbed insulation also produced cabling withpoor electrical properties. The spaces between ribs may be contaminatedwith dirt and water. These contaminants negatively affect the DK of theinsulated conductor because the contaminants have DKs that are widelyvarying and typically much higher then the insulation material. Thevarying DKs of the contaminants will give the overall insulatedconductor a DK that varies along its length, which will in turnnegatively affect signal speed. Likewise, contaminants with higher DKwill raise the overall DK of the insulation, which also negativelyaffects signal speed.

Insulated conductors with ribbed and channeled insulation also producedcabling with poor physical properties, which in turn degraded theelectrical properties. Because of the limited amount of material nearthe exterior surface of ribbed and known channeled insulation, suchinsulated conductors have unsatisfactorily low crush strengths; so lowthat the insulated conductors may not even be able to be spooled withoutdeforming the ribs and channels of the insulation. From a practicalstandpoint, this is unacceptable because it makes manufacture, storageand installation of this insulated conductor nearly impossible.

The crushing of the ribs and channels or otherwise physically stressingthe insulation, will change the shape of these features. This willnegatively influence the DK of insulation. One type of physicalstressing that is a necessary part of cabling is twisting a pair ofinsulated conductors together. This type of torsional stress cannot beavoided. Thus, the very act of making a twisted pair may severelycompromise the electrical properly of these insulated conductors.

Another area of concern in the wire and cable field is how the wireperforms in a fire. The National Fire Prevention Association (NFPA) setstandards for how materials used in residential and commercial buildingburn. These tests generally measure the amount of smoke given off, thesmoke density, rate of flame spread and/or the amount of heat generatedby burning the insulated conductor. Successfully completing these testsis an aspect of creating wiring that is considered safe under modernfire codes. As consumers become more aware, successful completion ofthese tests will also be a selling point.

Known materials for use in the insulation of wires, such asfluoropolymers, have desirable electrical properties such as low DK. Butfluoropolymers are comparatively expensive. Other compounds are lessexpensive but do not minimize DK, and thus delay skew, to same extent asfluoropolymers. Furthermore, non-fluorinated polymers propagate flameand generate smoke to a greater extent than fluoropolymers and thus areless desirable material to use in constructing wires.

Thus, there is a need for a wire that addresses the limitations of theprior art to effectively minimize delay skew and provide high rates oftransmission while also being cost effective and clean burning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective, stepped cut away view of a wire according tothe present invention.

FIG. 2 shows a cross-section of a wire according to the presentinvention.

FIG. 3 shows a cross-section of another wire according to the presentinvention.

FIG. 4 shows a perspective view of an extrusion tip for manufacturing awire according to the present invention.

FIG. 5 shows a perspective view of another extrusion tip formanufacturing a wire according to the present invention.

FIG. 6 shows a cross-section of a wire with a channeled jacket accordingto the present invention.

FIG. 7 shows a cross-section of a wire with a channeled conductoraccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The wire of the present invention is designed to have a minimizeddielectric constant (DK). A minimized DK has several significant effectson the electrical properties of the wire. Signal throughput is increasedwhile signal attenuation is decreased. In addition, delay skew intwisted pair applications is minimized. The minimized DK is achievedthrough the utilization of an improved insulated conductor or isolatedcore as described below.

A wire 10 of the present invention has a conductor 12 surrounded by aprimary insulation 14, as shown in FIG. 1. Insulation 14 includes atleast one channel 16 that runs the length of the conductor. Multiplechannels may be circumferentially disposed about conductor 12. Themultiple channels are separated from each other by legs 18 ofinsulation. The individual wires 10 may be twisted together to form atwisted pair. Twisted pairs, in turn, may be twisted together to form amulti-pair cable. Any plural number of twisted pairs may be utilized ina cable. Alternately, the channeled insulation may be used in coaxial,fiber optic or other styles of cables. An outer jacket 20 is optionallyutilized in wire 10. Also, an outer jacket may be used to cover atwisted pair or a cable. Additional layers of secondary, un-channeledinsulation may be utilized either surrounding the conductor or at otherlocations within the wire. In addition, twisted-pairs or cables mayutilize shielding.

The cross-section of one aspect of the present invention is seen in FIG.2. The wire 10 includes a conductor 12 surrounded by an insulation 14.The insulation 14 includes a plurality of channels 16 disposedcircumferentially about the conductor 12 that are separated from eachother by legs 18. Channels 16 may have one side bounded by an outerperipheral surface 19 of the conductor 12. Channels 16 of this aspectgenerally have a cross-sectional shape that is rectangular.

The cross-section of another aspect of the present invention is seen inFIG. 3. The insulation 14′ includes a plurality of channels 16′ thatdiffer in shape from the channels 16 of the previous aspect.Specifically, the channels 16′ have curved walls with a flat top. Likethe previous aspect, the channels 16′ are circumferentially disposedabout the conductor 12 and are separated by legs 18′. Also in thisaspect, the insulation 14′ may include a second plurality of channels22. The second plurality of channels 22 may be surrounded on all sidesby the insulation 14′. The channels 16′ and 22 are preferably used incombination with each other.

The channeled insulation protects both the conductor and the signalbeing transmitted thereon. The composition of the insulation 14, 14′ isimportant because the DK of the chosen insulation will affect theelectrical properties of the overall wire 10. The insulation 14, 14′ ispreferably an extruded polymer layer that is formed with a plurality ofchannels 16, 16′ separated by intervening legs 18, 18′ of insulation.Channels 22 are also preferably formed in the extruded polymer layer.

Any of the conventional polymers used in wire and cable manufacturingmay be employed in the insulation 14, 14′, such as, for example, apolyolefin or a fluoropolymer. Some polyolefins that may be used includepolyethylene and polypropylene. However, when the cable is to be placedinto a service environment where good flame resistance and low smokegeneration characteristics are required, it may be desirable to use afluoropolymer as the insulation for one or more of the conductorsincluded in a twisted pair or cable. While foamed polymers may be used,a solid polymer is preferred because the physical properties aresuperior and the required blowing agent can be eliminated.

In addition, fluoropolymers are preferred when superior physicalproperties, such as tensile strength or elongation, are required or whensuperior electrical properties, such as low DK or attenuation, arerequired. Furthermore, fluoropolymers increase the crush strength of theinsulated conductor, while also providing an insulation that isextremely resistant to invasion by contaminants, including water.

As important as the chemical make up of the insulation 14, 14′ are thestructural features of the insulation 14, 14′. The channels 16, 16′ and22 in the insulation generally have a structure where the length of thechannel is longer than the width, depth or diameter of the channel. Thechannels 16, 16′ and 22 are such that they create a pocket in theinsulation that runs from one end of the conductor to the other end ofthe conductor. The channels 16, 16′ and 22 are preferably parallel to anaxis defined by the conductor 12.

Air is preferably used in the channels; however, materials other thanair may be utilized. For example, other gases may be used as well asother polymers. The channels 16, 16′ and 22 are distinguished from otherinsulation types that may contain air. For example, channeled insulationdiffers from foamed insulation, which has closed-cell air pockets withinthe insulation. The present invention also differs from other types ofinsulation that are pinched against the conductor to form air pockets,like beads on a string. Whatever material is selected for inclusion inthe channels, it is preferably selected to have a DK that differs fromthe DK of the surrounding insulation.

Preferably, the legs 18, 18′ of the insulation 14, 14′ abut the outerperipheral surface 19 of the conductor 12. In this way, the outerperipheral surface 19 of the conductor 12 forms one face of the channel,as seen in FIGS. 1-3. At high frequencies, the signal travels at or nearthe surface of the conductor 12. This is called the ‘skin effect’. Byplacing air at the surface of the conductor 12, the signal can travelthrough a material that has a DK of 1, that is, air. Thus, the area thatthe legs 18, 18′ of the insulation 14, 14′ occupy on the outerperipheral surface 19 of the conductor 12 is preferably minimized. Thismay be accomplished by maximizing the cross-sectional area of thechannels 16, 16′, and consequently minimizing the size of legs 18, 18′,utilized in the insulation 14, 14′. Also, the shape of the channels 16,16′ may be selected to minimize the legs 18, 18′ contact area with theconductor 12 and to increase the strength of the channels.

A good example of maximizing cross-sectional area and minimizing theoccupied area can be seen in FIG. 3, where channels 16′ with curvedwalls are utilized. The walls curve out to give channels an almosttrapezoidal shape. The almost trapezoidal channels 16′ have largercross-sectional areas than generally rectangular channels 16.Furthermore, the curve walls of adjacent channels cooperate to minimizethe size of the leg 18′ that abuts the outer peripheral surface 19 ofthe conductor 12.

Furthermore, the area that the legs 18, 18′ of the insulation 14 occupyon the outer peripheral surface 19 of the conductor 12 can be minimizedby reducing the number of channels 16, 16′ utilized. For example insteadof the six channels 16, 16′ illustrated in FIGS. 2-3, five or fourchannels may be used.

Preferably, the area occupied by the legs 18, 18′ on the outerperipheral surface 19 of the conductor 12 is less than about 75% of thetotal area, with legs that occupy less than about 50% being morepreferred. Insulation with legs that occupy about 35% of the area ofouter peripheral surface is most preferred, although areas as small as15% may be suitable. In this way, the area of the outer peripheralsurface where the signal can travel through air is maximized. Statedalternatively, by minimizing the area occupied by the legs, the skineffect is maximized.

A good example of increasing strength through channel shape is throughthe use of an arch. An arch has an inherent strength that improves thecrush resistance of the insulated conductor, as discussed in more detailbelow. Arch shaped channels may also have economic benefits as well. Forexample, because the insulation is stronger, less insulation may beneeded to achieve the desired crush resistance. The channels may haveother shapes that are designed to increase the strength of the channels.

The channels 22 also minimize the overall DK of the insulation 14′ byincluding air in the insulation 14′. Furthermore, the channels 22 can beutilized without compromising the physical integrity of the wire 10.

The cross-sectional area of the channels should be selected to maintainthe physical integrity of wire. Namely, it is preferred that any onechannel not have a cross-sectional area greater than about 30% of thecross-sectional area of the insulation.

Through the use of the wire 10 with channeled insulation 14, 14′, adelay skew of less than 20 ns is easily achieved in twisted pair ormulti-pair cable applications, with a delay skew of 15 ns preferred. Adelay skew of as small as 5 ns is possible if other parameters, e.g. laylength and conductor size, are also selected to minimize delay skew.

Also, the lowered DK of the insulation 14, 14′ is advantageous when usedin combination with a cable jacket. Typically, jacketed plenum cablesuse a fire resistant PVC (FRPVC) for the outer jacket. FRPVC has arelatively high DK that negatively affects the impedance and attenuationvalues of the jacketed cable, but it is inexpensive. The insulation 14,14′, with its low DK, helps to offset the negative effects of the FRPVCjacket. Practically, a jacketed cable can be given the impedance andattenuation values more like an unjacketed cable.

Indeed, the low DK provided by the insulation 14, 14′ also increases thesignal speed on the conductor, which, in turn, increases the signalthroughput. Signal throughput of at least 450 ns for 100 meters oftwisted pair is obtained, while signal speeds of about 400 ns arepossible. As signal speeds increase, however, the delay skew must beminimized to prevent errors in data transmission from occurring.

Furthermore, since the DK of the channeled insulation is proportional tothe cross-sectional area of the channels, the signal speed in a twistedpair is also proportional to the cross-sectional area of the channelsand thus easily adjustable. The lay length, conductor diameter, and theinsulator thickness need not be changed. Rather, the cross-sectionalarea of the channels can be adjusted to obtain the desired signal speedin balance with other physical and electrical properties of the twistedpair. This is particularly useful in a multi-pair cable. The delay skewof the cable may be thought of as the difference in signal speed betweenthe fastest twisted pair and the slowest twisted pair. By increasing thecross-sectional area of the channels in the insulation of the slowesttwist pair, its signal speed can be increased and thus more closelymatched to the signal speed of the fastest twisted pair. The closer thematch, the smaller the delay skew.

As compared to un-channeled insulation, channeled insulation has areduced dissipation factor. The dissipation factor reflects the amountof energy that is absorbed by the insulation over the length of the wireand relates to the signal speed and strength. As the dissipation factorincreases, the signal speed and strength decrease. The skin effect meansthat a signal on the wire travels near the surface of the conductor.This also happens to be where the dissipation factor of the insulationis the lowest so the signal speed is fastest here. As the distance fromthe conductor increases, the dissipation factor increases and the signalspeed begins to slow. In an insulated conductor without channels, thedifference in the dissipation factor is nominal. With the addition ofchannels to the insulation, the dissipation factor of the insulationdramatically decreases because of the lower DK of the medium throughwhich the signal travels. Thus, incorporation of channels creates asituation where the signal speed in the channels is significantlydifferent, i.e. faster, than the signal speed in the rest of theinsulation. Effectively, an insulated conductor is created with twodifferent signal speeds where the signal speeds can differ by more thanabout 10%.

Placement of the channels 16, 16′ adjacent to the outer peripheralsurface 19 of the conductor 12 also does not compromise the physicalcharacteristics of the insulated conductor, which in turn preserves theelectrical properties of the insulated conductor. Because the exteriorsurface of the insulated conductor is intact, there is no opportunityfor contaminants to become lodged in the channels. The consequence isthat the DK of the insulation does not vary over the length of the cableand the DK is not negatively affected by the contaminants.

By placing the channels near the conductor, the crush strength of theinsulated conductor is not compromised. Namely, sufficient insulation isin place so that the channels are not easily collapsed. Further, theinsulation also prevents the shape of the channels from beingsignificantly distorted when torsional stress is applied to theinsulated conductor. Consequently, normal activities, i.e., manufacture,storage and installation, do adversely affect the physical properties,and be extension, the electrical properties, of insulated conductor ofthe present invention.

Besides the desirable effects on the electrical properties of the wire10, the insulation 14, 14′ has economic and fire prevention benefits aswell. The channels 16, 16′ and 22 in the insulation 14, 14′ reduce thematerials cost of manufacturing the wire 10. The amount of insulationmaterial used for the insulation 14, 14′ is significantly reducedcompared to non-channeled insulation and the cost of the filler gas isfree. Stated alternately, more length of the insulation 14, 14′ can bemanufactured from a predetermined amount of starting material whencompared to non-channeled insulation. The number and cross-sectionalarea of the channels 16, 16′ and 22 will ultimately determine the sizeof the reduction in material costs.

The reduction in the amount of material used in the insulation 14, 14′also reduces the fuel load of the wire 10. Insulation 14, 14′ gives offfewer decomposition by-products because it has comparatively lessinsulation material per unit length. With a decreased fuel load, theamount of smoke given off and the rate of flame spread and the amount ofheat generated during burning are all significantly decreased and thelikelihood of passing the pertinent fire safety codes, such as NFPA 255,259 and 262, is significantly increased. A comparison of the amount ofsmoke given off and the rate of flame spread may be accomplished throughsubjecting the wire to be compared to a UL 910 Steiner Tunnel burn test.The Steiner Tunnel burn test serves as the basis for the NFPA 255 and262 standards. In every case, a wire with channeled insulation where thechannels contain air will produce at least 10% less smoke then wire withun-channeled insulation. Likewise, the rate of flame spread will be atleast 10% less than that of un-channeled insulation.

A preferred embodiment of the present invention is a wire 10 withinsulation 14, 14′ made of fluoropolymers where the insulation is lessthan about 0.010 in thick, while the insulated conductor has a diameterof less than about 0.042 in. Also, the overall DK of the wire ispreferably less than about 2.0, while the channels have across-sectional are of at least 2.0×10⁻⁵ in².

The preferred embodiment was subjected to a variety of tests. In a testof water invasion, a length of channeled insulated conductor was placedin water heated to 90° C. and held there for 30 days. Even under theseadverse conditions, there was no evidence of water invasion into thechannels. In a torsional test, a 12 inch length of channeled insulatedconductor was twisted 180° about the axis of the conductor. The channelsretained more than 95% of their untwisted cross-sectional area. Similarresults were found when two insulated conductors were twisted together.In a crush strength test, the DK of a length of channeled insulatedconductor was measured before and after crushing. The before and afterDK of the insulated conductor varied by less the 0.01.

While the insulation is typically made of a single color of material, amulti-colored material may be desirable. For instance, a stripe ofcolored material may be included in the insulation. The colored stripeprimarily serves as a visual indicator so that several insulatedconductors may be identified. Typically, the insulation material isuniform with only the color varying between stripes, although this neednot be the case. Preferably, the stripe does not interfere with thechannels.

Examples of some acceptable conductors 12 include solid conductors andseveral conductors twisted together. The conductors 12 may be made ofcopper, aluminum, copper-clad steel and plated copper. It has been foundthat copper is the optimal conductor material. In addition, theconductor may be glass or plastic fiber, such that fiber optic cable isproduced.

The wire may include a conductor 72 that has one or more channels 74 inits outer peripheral surface 76, as seen in FIG. 7. In this particularaspect of the invention, the channeled conductor 72 is surrounded byinsulation 78 to form an insulated, channeled conductor 80. Theindividual insulated conductors may be twisted together to form atwisted pair. Twisted pairs, in turn, may be twisted together to form amulti-pair cable. Any plural number of twisted pairs may be utilized ina cable.

The one or more channels 74 generally run parallel to the longitudinalaxis of the wire, although this is not necessarily the case. With aplurality of channels 74 arrayed on the outer peripheral surface 76 ofthe conductor 72, a series of ridges 82 and troughs 84 are created onthe conductor.

As seen in FIG. 7, the channeled conductor 72 may be combined withchanneled insulation 78, although this is not necessarily the case. Thelegs 86 of the channeled insulation 78 preferably contact the channeledconductor 72 at the ridges 82. This alignment effectively combines thechannels 88 of the insulation 78 with the channels 74 of the conductor,creating a significantly larger channel. The larger channel may resultin a synergistic effect that enhances the wire beyond the enhancementsprovided by either channeled insulation or channeled conductorindividually.

A channeled conductor has two significant advantages over smoothconductors. First, the surface area of the conductor is increasedwithout increasing the overall diameter of the conductor. Increasedsurface area is important because of the skin effect, where the signaltravels at or near the outer peripheral surface of the conductor. Byincreasing the surface area of the conductor, the signal is able totravel over more area while the size of the conductor remains the same.Compared to a smooth conductor, more signal can travel on the channeledconductor. Stated alternatively, a channeled conductor has more capacityto transmit data than a smooth conductor. Second, the use of air orother low DK material in the channels of the conductor reduces theeffective DK of the wire including channeled conductors. As discussedabove with the channeled insulation, the lower overall DK of the wire isadvantageous for several reasons including increased signal speed andlower attenuation and delay skew. Furthermore, the use of a low DKmaterial, e.g., air, in the channels of the conductor also enhances theskin effect of signal travel. This means that the signal travel fasterand with less attenuation. Taken together, the two advantages ofchanneled conductors over smooth conductors create a wire that has morecapacity and a faster signal speed.

Channeled conductors also have other incidental advantages over smoothconductors such as reduced material cost because more length of thechanneled conductor can be manufactured from a predetermined amount ofstarting material when compared to non-channeled or smooth conductor.The number and cross-sectional area of the channels will ultimatelydetermine the size of the reduction in material costs.

The outer jacket 20 may be formed over the twisted wire pairs and as cana foil shield by any conventional process. Examples of some of the morecommon processes that may be used to form the outer jacket includeinjection molding and extrusion molding. Preferably, the jacket iscomprised of a plastic material, such as fluoropolymers, polyvinylchloride (PVC), or a PVC equivalent that is suitable for communicationcable use.

As noted above the wire of the present invention is designed to have aminimized DK. In addition to the use of channeled insulation andconductor, a wire with a minimized DK can be achieved through theutilization of an improved isolated core. Like the insulation andconductor, the wire may include an outer jacket 50 that includeschannels 52, as seen in FIG. 6. In this particular aspect of theinvention, the channeled jacket 50 surrounds a core element 54 to forman isolated core 56. The core element is at least one insulatedconductor; typically, the core element includes a plurality oftwisted-pairs. Additionally, the core element may include anycombination of conductors, insulation, shielding and separators aspreviously discussed. For example, FIG. 6 shows an isolated core 56 withfour twisted pairs 58, 60, 62 and 64 twisted around each other andsurrounded by a channeled jacket 50.

Generally, the entire discussion above concerning the chemical andstructural advantages for channeled insulation also pertains tochanneled jackets; that is, a jacket with a low DK is desirable for thesame reasons an insulation with a low DK is desirable. The low DK of thejacket imparts to the wire similar advantageous physical, electrical andtransmission properties as the channeled insulation does. For example,the channels in the jacket lower the overall DK of the jacket, whichincreases signal speed and decreases attenuation for the jacketed wireas a whole. Likewise, the dissipation factor of the jacket issignificantly reduced through the use of channels, thus increasingsignal speed near the core element. The signal speed away from the coreelement is not increased as much, thus giving a wire that effectivelyhas two different signal speeds; an inner signal speed and an outersignal speed. The difference in signal speed may be significant; e.g.the inner signal speed may be may be more than about 2% faster than theouter signal speed. Preferably, the difference in signal speed is on theorder of about 5%, 10% or more. Stately alternatively, the channeledjacket may have more than one DK such that the jacket includesconcentric portions that have different DKs and thus different signalspeeds. In addition to the speed differences observed in the jacket,differences in signal speed may also be observed between inner and outerportions of channeled insulation.

The dissipation factor of the jacket or insulation may be adjusted byselecting a composite density of the materials for the inner portion andthe outer portion. As the name suggests, the composite density is theweight of material, either insulation or jacket, for a given volume ofmaterial. A material with a lower composite density will have a lowerdissipation factor as compared with a higher composite density. Forexample, a channeled jacket where the channels contain air will have amuch lower composite density than an un-channeled jacket. In thechanneled jacket, significant portions of the jacket material isreplaced by much lighter air, thus reducing the composite density of thejacket, which in turn reduces the dissipation factor of the jacket.Differences in composite density may be accomplished with means otherthan channels in the jacket or insulation.

As with the channeled insulation, it is desirable to maximizecross-sectional area of the channels in the jacket, minimize the areathe legs of the jacket occupy on the core element, all the whilemaintaining the physical integrity of the wire. Fire protection andeconomic advantages are also seen with channeled jackets as comparedun-channeled jackets.

In a wire with a preferred balance of properties, the channeled jackethas a plurality of channels, but no one of the channels has across-sectional of greater than about 30% of the cross-sectional area ofthe jacket. Furthermore, the preferred channel has a cross-sectionalarea of at least 2.0×10⁻⁵ in². One useful wire has an isolated corediameter of less than about 0.25 in, while the preferred channeledjacket thickness is less than about 0.030 in.

In a preferred aspect of the present invention, the wire includes one ormore components with channels, such that the wire includes a channeledconductor, channeled insulation or a channeled jacket. In a mostpreferred aspect, the wire includes a combination of channeledcomponents, including those embodiments where all three of theconductor, insulation and jacket are channeled. When the channeledcomponents are used in combination, a wire is achieved that has a DKthat is significantly less than a comparably sized wire withoutchannels.

The present invention also includes methods and apparatuses formanufacturing wires with channeled insulation. The insulation ispreferably extruded onto the conductor using conventional extrusionprocesses, although other manufacturing processes are suitable. In atypical insulation extrusion apparatus, the insulation material is in aplastic state, not fully solid and not fully liquid, when it reaches thecrosshead of the extruder. The crosshead includes a tip that defines theinterior diameter and physical features of the extruded insulation. Thecrosshead also includes a die that defines the exterior diameter of theextruded insulation. Together the tip and die help place the insulationmaterial around the conductor. Known tip and die combinations have onlyprovided an insulation material with a relatively uniform thickness at across-section with a tip that is an unadulterated cylinder. The goal ofknown tip and die combinations is to provide insulation with a uniformand consistent thickness. In the present invention, the tip providesinsulation with interior physical features; for example, channels. Thedie, on the other hand, will provide an insulation relatively constantexterior diameter. Together, the tip and die combination of the presentinvention provides an insulation that has several thicknesses.

The insulation 14 shown in FIG. 2 is achieved through the use of anextrusion tip 30 as depicted in FIG. 4. The tip 30 includes a bore 32through which the conductor may be fed during the extrusion process. Aland 34 on the tip 30 includes a number of grooves 36. In the extrusionprocess, the tip 30, in combination with the die, fashions theinsulation 14 that then may be applied to the conductor 12.Specifically, in this embodiment, the grooves 36 of the land 34 createthe legs 18 of the insulation 14 such that the legs 18 contact theconductor 12 (or a layer of an un-channeled insulation). The prominences38 between the grooves 36 on the land 34 effectively block theinsulation material, thus creating the channels 16 in the insulationmaterial as it is extruded.

The insulation 14′ shown in FIG. 3 is achieved through the use of anextrusion tip as depicted in FIG. 5. The tip 30′ includes a bore 32through which the conductor may be fed during the extrusion process.Like the tip of FIG. 4, the land 34 of the tip 30′ includes a number ofgrooves 36′ separated by prominences 38′. In this embodiment, thegrooves 36′ are concave, while the prominences 38′ are flat topped.Together, the grooves 36′ and prominences 38′ of the land 34 form convexlegs 18′ and flat-topped channels 16′ of the insulation. In addition,the tip 30′ also includes a number of rods 40 spaced from the land 34.The rods 40 act similar to the prominences 38′ and effectively block theinsulation material, thus creating long channels 22 surrounded byinsulation 14′, as seen in FIG. 3.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis by way of illustration and not of limitation, and the scope of theappended claims should be construed as broadly as the prior art willpermit.

1. A data transmission cable comprising: four or fewer twisted pairs ofdata transmission conductors; and a jacket within which the four orfewer twisted pairs of data transmission conductors are located, thejacket defining interior channels that are circumferentially spacedrelative to one another about the four or fewer of twisted pairs of datatransmission conductors, the interior channels defining legsthereinbetween that project inwardly toward a central axis of thejacket, the legs being attached to the jacket at outer ends and the legshaving free, unattached inner ends, the interior channels each having anopen end that faces inwardly toward the central axis of the jacket and aclosed end, wherein at least a portion of the closed end defines atleast one rounded corner adjoining two intersecting sides of thechannel, the rounded corner formed by being extruded through anextrusion tip that includes at least one rounded tip surface, the fouror fewer twisted pairs of data transmission conductors being exposed toair within the interior channels, the four or fewer twisted pairs ofdata transmission conductors generally not occupying the interiorchannels.
 2. The cable of claim 1, wherein each of the data transmissionconductors of the four or fewer twisted pairs of data transmissionconductors is covered by a separate insulation layer.
 3. The cable ofclaim 1, wherein number of interior channels is greater than the numberof twisted pairs of data transmission conductors.
 4. The cable of claim1, wherein each of the interior channels has a cross-sectional area lessthan about 30 percent of a total cross-sectional area of the jacket. 5.A method of extruding an outer jacket of a data transmission cablehaving a plurality of twisted pairs of conductors, wherein the outerjacket defines a central passage in which the plurality of twisted pairsof conductors is located, the central passage including air, the air inthe central passage occupying a volume between the plurality of twistedpairs of conductors, the jacket including legs that project inwardlytoward the central axis of the cable, the jacket defining channelslocated between the legs, the channels including air, the air in thechannels being in fluid communication with the air in the centralpassage that occupies the volume between the plurality of twisted pairsof conductors, wherein each of the channels is defined by at least onecurved surface, the method comprising: providing an extrusion tip thatincludes a bore and a land defining a number of radially arrangedgrooves and a number of radially arranged prominences, wherein eachprominence defines at least one curved surface; feeding the conductorsthrough the bore; and extruding jacket material through the radiallyarranged grooves, wherein the at least one curved surface defining eachchannel is formed by the at least one curved surface of each prominence.6. A cable having a central axis, the cable comprising: a plurality oftwisted pairs of conductors; and an extruded jacket defining a centralpassage in which the plurality of twisted pairs of conductors islocated, the central passage including air, the air in the centralpassage occupying a volume between the plurality of twisted pairs ofconductors, the jacket including legs that project inwardly toward thecentral axis of the cable, the jacket defining channels located betweenthe legs, the channels including air, the air in the channels being influid communication with the air in the central passage that occupiesthe volume between the plurality of twisted pairs of conductors, whereinwhen the cable is viewed in a transverse cross-section, each of thechannels is defined by a surface provided with a curvature that isformed during the extrusion process, the channels having lengths thatrun along a length of the jacket, and the number of channels beinggreater than the number of twisted pairs of conductors.
 7. The cable ofclaim 6, wherein the plurality of twisted pairs of conductors includes 4twisted pairs of conductors.
 8. The cable of claim 6, wherein each ofthe conductors of the plurality of twisted pairs of conductors iscovered by a separate insulation layer.
 9. The cable of claim 6, whereinthe twisted pairs of conductors generally do not occupy the channels.10. The cable of claim 6, wherein the plurality of twisted pairs ofconductors are twisted around each other to define a core, the coreincluding a separator.